Amp Glow
A coloured brightening at one edge or corner of a long exposure, caused by heat and stray light from on-chip electronics.
In depth
Readout amplifiers emit a small amount of infrared as they operate, and over a long exposure the nearby photosites record it. The result is a magenta or amber gradient in a predictable location. Because it is consistent, dark frame subtraction removes it cleanly, and modern sensor designs suppress it well.
Examples in practice
A ten-minute exposure shows a magenta wash creeping in from the left edge that a dark frame subtracts entirely.